This invention relates to a pipe having a replaceable wear resistant lined coupler and particularly to such pipe for carrying abrasive and wear creating materials, in particular, concrete.
Concrete pumping is used in placement of concrete in various applications. The present invention has been particularly applied to the concrete pumping technology but is equally applicable to other transport of highly abrasive material through a piping system. In concrete pumping as well as other abrasive material transport, excessive wear of the pipe is a common problem, and a special problem at the coupling of pipe sections, particularly where there is a change of flow direction.
In concrete pumping systems, initial pipe sections are interconnected to each other with releasable couplings. A typical system is disclosed in U.S. Pat. No. 3,705,737, which issued December, 1972 and U.S. Pat. No. 4,305,607 which issued Dec. 15, 1981, to the assignee of this invention. The couplings of the pipes generally in present technology include a releasable C-shaped clamp or the like with a sealing gasket located within the coupling to seal the joint between slightly spaced pipe ends. Thus, the pipe ends will normally be spaced slightly from each other and sealed by the outer special gasket structures. The pipe ends universally include an annular groove with the side edges of the clamp members fitting within the grooves, and locking the pipes to each other. Where a change of direction is required in the flow of the concrete, metal pipe elbows are connected to the straight pipe sections.
All of the pipe connections present areas which are particularly subject to significant wear as a result of abrasive characteristic of concrete, and will exist with other abrasive semi-solid flowing materials. The grooved areas of each pipe coupling presents areas of greatest weakness. Further, when the end coupling assembly is worn, the pipe section must be replaced. The elbows in the flow system also present a particularly severe area of wear at the outer elbow wall facing the oncoming stream of material as a result of the continuous engagement of the solid particles within the concrete or other fluid particle borne fluid moving into turning engagement with such wall. In the concrete pumping art and the like the releasable coupling system used as an industry standard creates a relatively weak wear area. The pipe coupling systems include a pipe end construction including the annular coupling groove. The coupling groove creates a substantially thinner wall in the pipe section configuration. In such standard coupling systems, a particularly severe problem of premature failure is thereby created in the area of the relatively thin wall. This type of coupling, however, has been used for many years, and is highly desirable because of many other reasons.
To minimize the necessity for frequent replacement of pipe sections and particularly elbows, the pipe may be specially formed with an inner wall to withstand an abrasive characteristic. Thus, the inner wall may be specially hardened or provided with a highly abrasive resistant inner liner. Various ceramic materials have in particular been used. An advantageous dual metal wall structure which provides a high, wear resistant inner liner is disclosed in the U.S. Pat. No. 5,097,585 which issued Mar. 24, 1992 to the assignee of this invention. The assignee of this invention has employed ceramic lining in the metal pipe sections including elbows. The liners are preferably constructed with the ceramic liner formed as individual segments which are adhesively mounted for replacement. This permits the repair of elbows which have been worn as a result of the abrasive characteristic in such a manner as to minimize the overall costs associated with the transport of abrasive materials.
The ceramic lined elbows and pipe, however, include a continuing problem of failure at the ends or interface area because of the turbulent flow characteristics and the physical restrictions created by the standard coupling configuration. In addition, a hard-face material has been welded within the pipe at the connections or couplings to increase the life at such critical areas. Although this process increased the life expectancy, the overall results were commercially disadvantages from the standpoint of costs in that the material and its application were expensive. Further, such structure is not adapted to cost effective field repair or replacement.
Other prior art has suggested other solutions. Thus, for example, U.S. Pat. No. 5,044,670 which issued Sep. 3, 1991 discloses an end liner or insert for interconnection to a pipe end in a concrete pumping system, the patent discloses an extended coupler member welded to the exterior of a metal pipe with the coupling member projecting outwardly from the pipe end. The member has an inclined circumferential wall or roof projecting outwardly from the pipe, with an insert clamped therein. The insert is replaceably clamped in the outer member in a positive locking and frictionally engaging manner. The insert projects inwardly of the diameter of the pipe and provides a reduced diameter opening for the inner connection of an elbow, or alternatively, an aligned common diameter between the insert and the downstream piping. The inwardly projecting insert is used to provide withdrawal of the insert for use of a suitable tool. In the common diameter structure, a gap is introduced between the insert and the end of the pipe to permit the removal of the insert member through the use of a suitable gap-engaging tool.
Thus, although the various problems have been well recognized and various solutions suggested and used, there is a continuing need for a more cost effective solution to the problem of the wear characteristic created by the flow of abrasive materials, particularly at pipe connecting joints.
The present invention is particularly directed to a superior wear resistant pipe structure for carrying of high abrasive materials and particularly to an end insert of a superior wear-resistant construction and configuration and to the method of application. Generally, in accordance with the present invention, a special hard wear-resistant insert liner is formed of a special hardened material, such as a special carbide material, a special ceramic material or the like. The hard wear-resistant end insert liner is secured within a recessed end of the pipe and particularly in an end coupler section or member. The insert liner is, in one aspect of this invention, adhesively bonded in place and subject to release using heat or other operative energy field to soften or otherwise effectively release the adhesive and permit ready removal of the insert liner as well as the adhesive. This solution provides not only a rapid and cost effective formation of the pipe structure with the necessary wear resistant characteristic but permits quick inexpensive replacement of the insert liner.
In accordance with another feature of the present invention, the insert liner is specially constructed as a cast member with an exterior and internal surface to provide optimal casting while maintaining maximum hardened material within the coupling. Generally, the liner includes a fixed inner connecting or transfer area or section having a diameter which is preferably slightly less than the pipe diameter and with an inward taper from the outer end of the insert liner to such connecting section and an outward taper from such connecting section to the pipe.
More particularly, in one aspect of the invention, the insert liner is preferably formed by casting and particularly of a cast chrome-iron alloy which produces carbides of a high degree of hardness and preferably in a range of 80 to 90 Rockwell hardness. The alloy in one preferred embodiment includes significant chrome and carbon and traces of nickel, molybdenum and silicon. The cast chrome-iron alloy is an alloy having a microstructure that consists essentially of carbides, martensite, bainite and austenite. Various high toughened ceramic materials which have a Rockwell hardness in the range of 80 to 90 are available and are distinct from thermal insulating ceramics. The toughened ceramics can be used as the liner, but generally require preforming, machining and then firing. The present limitations on the ceramic casting technology limits the cost effective commercial usage of ceramic materials.
In another aspect of the present invention, the coupling end structure may be formed integrally with the pipe or as a separate coupler having a body member welded to the pipe.
The insert liner is generally formed as an L-shaped member having an outer flange adapted to abut the end of the body member of the coupler and an inwardly projecting tubular portion or member extended beneath the coupler and into abutting engagement with the end of the pipe. The outer diameter of the insert liner is tapered inwardly to define a slight but a distinct gap, which gap preferably increases from an outer portion of the tubular portion to the abutting pipe end. This increases the available space for the epoxy and provides optimum bonding characteristic, and allows easy insertion and removal. This feature further provides an improved casting characteristic. The leading edge or flange provides additional wear resistant material at the location of primary wear characteristics and also provides a mechanical interlock which will prevent the liner from dislodging and plugging the system in the event of excessive insert liner wear before replacement. The flange also minimizes casting time and requirements, creating a more round condition due to its configuration. The flange areas also permits the use of a puller or hammer to aid in removal of the insert liner, as well as providing a relatively strong outer wall so the insert liner can be tapped in with a hammer without breakage.
The present liner is equally applicable to any pipe section carrying highly abrasive materials including straight pipe sections, elbow sections, reducing sections and the like, and provides both a highly cost effective insert and additionally contributes to the useful operating life of the piping sections as a result of the convenient and relatively inexpensive field replacement.